1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method. More specifically, the present invention relates to an image forming apparatus and an image forming method of an intermediate transfer system in which an image is first formed on an intermediate transfer medium by an inkjet device and then transferred to a printing medium.
2. Description of the Related Art
Recording high quality images has been recently increasingly in demand in various fields regardless of the type of printing media while taking advantage of an inkjet recording system.
If, however, an image is formed on a printing medium to which ink is less permeable in the inkjet recording system, the formed image suffers from feathering, beading or bleeding, which may affect image quality. The printing medium suffers from problems, such as cockling, which is a ruffling phenomenon caused by water-based ink permeating the printing medium.
In order to overcome these problems, an intermediate transfer recording system has been proposed. In this recording system, an ink image is first formed on an intermediate transfer medium by application of ink in an inkjet recording system. The ink image formed on the intermediate transfer medium is then transferred to a printing medium. This recording system requires no rapid permeation and fixing of moisture content of the ink to the printing medium for the prevention of feathering, beading or bleeding and, therefore, the printing medium can be selected from among various options. Since most of liquid content of the ink constituting the ink image is removed before the ink image formed on the intermediate transfer medium is transferred to the printing medium, permeation of the liquid content into the printing medium is reduced. Also, occurrence of cockling is suppressed, thereby protecting the texture of the printing medium.
In the intermediate transfer recording system, the ink image formed on the intermediate transfer medium is pressed against the printing medium to cause the ink image to be transferred to the printing medium. If a printing medium with a coarse surface is used in the intermediate transfer recording system, there has been a problem of a “transfer residue.” In particular, a part of the ink image remains on the intermediate transfer medium without being transferred to the printing medium because of incomplete contact between the ink image and the printing medium.
As an approach to solve this problem, U.S. Pat. No. 7,281,790 proposes a method in which a resin-containing supplementary liquid is applied to an ink image formed on an intermediate transfer medium before and the ink image having the supplementary liquid applied thereto is transferred to a printing medium.
In the method disclosed in U.S. Pat. No. 7,281,790, the supplementary liquid is applied in accordance with logical sum data obtained from a logical sum of binary format image data corresponding to ink of four colors. This means that the supplementary liquid is applied only portions to which the ink has been applied. If the ink image has both high-duty portions and low-duty portions, the supplementary liquid is applied in a large amount to the high-duty portions while in a small amount to the low-duty portions. Such an approach does not reduce roughness on the ink image and, therefore, transferability of the ink image may be insufficient. In order to achieve sufficient transferability, it is desirable to make thickness of the ink image uniform as much as possible.